To find out more about Maya renderers, see the following:
When you select a renderer, Maya’s user interface is automatically configured to use the renderer. For example, if you render the current frame, Maya uses the renderer to process the image and display it in the Render View. Or, if you press the Display Render Settings window button, the Render Settings window appears, showing the Common tab and tab that corresponds to the selected renderer.
The mental ray renderer and the Maya Vector renderer are plug-ins that are loaded by default. If you do not see them listed in Render > Render Using, choose Window > Settings/Preferences > Plug-in Manager and make sure the Mayatomr and, or VectorRender plug-ins are loaded.
To specify the default renderer